After harvesting of potatoes or other tubers, said tubers are preserved at temperatures of approximately 20 to 30° C. for about 10 days in order to harden their peridermal layer (or “skin”), then gradually cooled to their preservation temperature, which is about 10° C.
During the first and second months following their harvest, the tubers remain in the rest state and exhibit few germination tendencies.
Nevertheless, before the end of this period, the tubers have to be chemically treated in order to inhibit germination, which would cause detrimental effects, such as loss in weight, preservation of the sugar starch, a decrease in the quality of the tubers and deterioration of their appearance. Furthermore, the sprouts and the surrounding tissues contain high levels of toxic glycoalkaloids, which are not destroyed during cooking.
The most commonly used anti-germination treatment processes employ chemical agents such as chloropropham, CIPC or 3-chlorophenylisopropylcarbamate. Generally, CIPC is applied to stored tubers using thermal fogging processes.
Generally, thermal fogging involves the application of CIPC by means of a hot air stream in order to produce an aerosol.
According to a first practice, the thermal fogging is carried out using pure CIPC. However, this process results in an unsatisfactory manner in the application of the pure active ingredient on the tubers. This is because the CIPC tends to form crystals and/or is not distributed uniformly on the tubers.
According to another practice, the CIPC is formulated in a solvent medium, such as methylene chloride or methyl alcohol. In this case, too, this process does not provide satisfactory results in so far as the solvents that are conventionally used have low boiling points and tend to evaporate rapidly during the thermal fogging. This results in the application of pure active ingredient having the same drawbacks as the preceding process.
Furthermore, CIPC dissolves with difficulty in conventional solvents, and maximum CIPC concentrations of approximately 30% (weight/volume) are generally obtained. At best, concentrations of approximately 54% at 180° C. have been obtained. This low solubility entails the use of large amounts of solvent and/or formulation in order to obtain the required amounts of active ingredient. Nevertheless, efforts are generally made to limit the use of these solvents owing to their inherent toxicity and/or the danger of use that they entail, especially as a result of their low boiling points, which result in high risks of flammability.
The use of synthetic derivatives for application to fruits and vegetables during growth or storage thereof is limited. CIPC levels, in particular are subject to increasingly stringent regulations. Accordingly, although CIPC is used to limit the formation of sprouts on the tubers, its toxicity might call into question its use at conventional application rates. It is accordingly desirable to limit as far as possible the amount of CIPC to be applied to bulbs and tubers.
Finally, available CIPC formulations exhibit poor stability, especially at low temperature, and this means that they are unsuitable for storage, especially in the cold stores for storing bulbs and/or tubers.
Attempts have been made to apply CIPC with terpene compounds in order to inhibit potato sprouts; more precisely. U.S. Pat. No. 5,811,372 relates to a method for the inhibition of tuber sprouts involving the application of CIPC and carvone. Nevertheless, the two agents are mixed in the composition to be applied. Furthermore, the same patent specifies that the combination of CIPC with similar derivatives (limonene or jasmone) does not produce positive results. Moreover, there is no indication of the effect of the carvone on the applicability and the distribution of the CIPC. Finally, there is no reference to the CIPC concentration levels being higher than those of the terpene.
It has now been discovered, and this is one of the subjects of the present invention, that terpenes and/or terpene oils, in particular eugenol, isoeugenol or clove oil, have a high capacity to dissolve CIPC, even in cases in which the two agents are applied separately. In particular, the use of terpenes and/or terpene oils of this type, applied before or after the CIPC, allows improved distribution of the CIPC on the potatoes. The separate application of the terpene or terpene oil therefore allows improved application, and accordingly penetration and efficacy, of the CIPC. It is thus possible to achieve CIPC concentrations of greater than 50% by weight of CIPC relative to the total volume of the solution, at ambient temperature and even at temperatures as low as 0° C. The process of the present invention therefore allows limitation of the amount of formulated product to be used.
It has also been discovered that the dissolving capacity of a terpene agent is also achieved if the CIPC is in “dry” form, i.e. if the CIPC was or is subsequently applied in pure form and if it is deposited in crystal form or in solution form, and if the solvent is evaporated during application or once it has been deposited on the bulb or tuber.
On the other hand, the process according to the invention uses terpenes or terpene oils having an elevated boiling temperature, preferably greater than 230° C., even more preferably greater than 240° C. This elevated boiling temperature thus allows the thermal fogging to be carried out at a higher temperature, providing an improved spray mist and therefore improved distribution on the treated bulbs and/or tubers. Also, the terpene compound or the oil does not decompose, or only decomposes slightly, and/or forms a high-quality mist during the thermal fogging, thus allowing improved distribution on the treated tuber.
Moreover, these elevated boiling points thus allow the risk of flammability to be reduced relative to the conventional solvents that are generally used in CIPC formulations, in which the solvents would be completely vaporised.
The terpenes and/or terpene oils exhibit suitable biocide activity against the fungi and bacteria that attack potatoes. They therefore allow the properties of the CIPC formulations to be improved.
Finally, the use of said terpenes and/or terpene oils, before or after the CIPC, maximises the anti-germination effect of the CIPC formulations.